In the construction of paved roadways the top wear layer often consists of a mixture of paving grade asphalt and aggregate. The asphalt employed for this purpose must be capable of readily being applied in molten condition, and the mixture must have flow values that are not so high as to allow the mix to distort easily under heavy loads, nor so low as to make the mix brittle and subject to cracking. Paving grade asphalts are sometimes blended with harder asphalts in order to extend the paving grade asphalt and to provide a commercial use for hard asphalts that otherwise have only limited use. One material which has been suggested as a suitable blend ingredient in a paving grade asphalt blend is a by-product of petroleum refining units utilizing a Residuum Oil Supercritical Extraction (ROSE) process. The by-product is a resin-asphaltene residuum that is very hard, with penetration of less than 10 at 77.degree. F. and a softening point above 150.degree. F., and has a high sulfur and metal content. The primary methods of disposing of this material have been to treat it as waste, with the concomitant problems of hazardous waste disposal, or to blend it with low-sulfur diesel and kerosene cutters to make a saleable fuel. Such fuel can be quite expensive, however, due to the value of the cutters, and may contain more sulfur than is desirable. Although use of the resin-asphalt residuum as a blend ingredient in asphalt paving is viable in certain minor amounts and under proper conditions, such use can account for the disposal of only minor amounts of the residuum.
The sub base, or base layer, of a paved roadway has different requirements than those of the surface layer. The road bed should be firm, yet flexible and compatible with the asphalt cover layer. Density and water penetration properties should be dictated by design. A common material used as a road bed is soil cement which, although initially inexpensive, is quite rigid and susceptible to cracking. The cracks reflect through the flexible surface layer, allowing water intrusion into the sub-base soils, which promotes further roadway deterioration. The introduction of water into a soil containing clay or other material that tends to become unstable when wet is especially detrimental.
It is an object of the invention to provide a suitable composition for sub base and base materials which will better meet the needs of the construction industry. Another object is to find a suitable large-scale use for resin-asphaltene residuum of the type referred to above.